Directional scan and connection mechanisms in wireless communications systems

ABSTRACT

A method in a wireless access point (AP) having an antenna controllable to transmit and receive using a set of AP sectors, includes: transmitting a plurality of beacon instances using each of the AP sectors, each beacon instance associated rotation schedule data defining a plurality of listening time slots corresponding to respective AP sectors; activating a rotating listening mode using the AP sectors in sequence according to the rotation schedule data; in response to detecting a sector sweep initiation message from a client device using an active one of the AP sectors, communicating with the client device to select an AP sector to use in establishing a link with the client device.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication No. 62/776,456, filed Dec. 6, 2018, the contents of which isincorporated herein by reference.

FIELD

The specification relates generally to wireless communications systems,and specifically to a method and system for implementing directionalscanning and connection mechanisms in wireless communications systems.

BACKGROUND

Some wireless communications systems, such as those implementedaccording to the Institute of Electrical and Electronics Engineers(IEEE) 802.11ad standard, employ beamforming between communicationdevices (e.g. between client devices and access points) to improvetransmission range and/or throughput. Before beamforming has beenperformed between two devices, either or both of the devices may awaitreceipt of initiation messages using an antenna configuration thatprovides a wider beam width than that employed for subsequentcommunications.

The greater beam width afforded by the above-mentioned antennaconfiguration, however, may reduce the reception sensitivity of theantenna. When the devices are sufficiently distant from one another, thedevice operating in the above antenna configuration may not detecttransmissions from the other device, preventing beamforming andsubsequent connection from being initiated.

SUMMARY

An aspect of the specification provides a method in a wireless accesspoint (AP) having an antenna controllable to transmit and receive usinga set of AP sectors, the method comprising: transmitting a plurality ofbeacon instances using each of the AP sectors, each beacon instanceassociated with rotation schedule data defining a plurality of listeningtime slots corresponding to respective AP sectors; activating a rotatinglistening mode using the AP sectors in sequence according to therotation schedule data; in response to detecting a sector sweepinitiation message from a client device using an active one of the APsectors, communicating with the client device to select an AP sector touse in establishing a link with the client device.

Another aspect of the specification provides an access point,comprising: an antenna array controllable to transmit and receive usinga set of AP sectors; a controller connected to the antenna array andconfigured to: control the antenna array to transmit a plurality ofbeacon instances using each of the AP sectors, each beacon instanceassociated with rotation schedule data defining a plurality of listeningtime slots corresponding to respective AP sectors; activate a rotatinglistening mode using the AP sectors in sequence according to therotation schedule data; and in response to detection of a sector sweepinitiation message from a client device using an active one of the APsectors, communicate with the client device to select an AP sector touse for establishing a link with the client device.

A further aspect of the specification provides a method in a wirelessclient device having an antenna controllable to transmit and receiveusing a set of client sectors, the method comprising: activating arotating listening mode using the client sectors in a predefinedsequence; in response to detecting a beacon from an access point (AP)associated with rotation schedule data defining a plurality of listeningtime slots corresponding to respective AP sectors of the AP, determininga transmission time based on the rotation schedule data; and at thetransmission time, transmitting a message to the AP.

A still further aspect of the specification provides a wireless clientdevice, comprising: an antenna array controllable to transmit andreceive using a set of client sectors; a controller connected to theantenna array and configured to: activate a rotating listening modeusing the client sectors in a predefined sequence; in response todetecting a beacon from an access point (AP) associated with rotationschedule data defining a plurality of listening time slots correspondingto respective AP sectors of the AP, determine a transmission time basedon the rotation schedule data; and at the transmission time, transmit amessage to the AP.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Embodiments are described with reference to the following figures, inwhich:

FIG. 1 is a diagram illustrating a wireless communication system;

FIG. 2 is a diagram illustrating example radiation patterns of antennaarrays in the system of FIG. 1;

FIG. 3 is a flowchart of a method for directional beam scanning andconnection;

FIGS. 4A, 4B and 4C are diagrams illustrating examples of rotationschedules employed in the method of FIG. 3;

FIG. 5 is a diagram illustrating an example structure for rotationschedule data defining the rotation schedules of FIGS. 4A-4C;

FIG. 6 is a diagram illustrating another example of a rotation scheduleemployed in the method of FIG. 3; and

FIG. 7 is a flowchart of an additional portion of the method of FIG. 3.

DETAILED DESCRIPTION

FIG. 1 depicts a wireless communications system 100, including aplurality of wireless devices. In particular, FIG. 1 illustrates anaccess point (AP) 104 connected with a client device 108 (also simplyreferred to as the client 108) via a wireless link 112. The access point104 can be, for example, a wireless router connecting the client device108 to a wide area network (not shown) such as the Internet. The accesspoint 104 may also be, for example, a media server, a home computer, amobile device, and the like. More generally, the AP 104 as referred toherein includes any wireless device implementing point coordinator (PC)functionality.

The client device 108, meanwhile, can be a mobile device such as asmartphone, a tablet computer and the like. The client device 108 mayalso be an access point itself, for example in implementations in whichthe devices 104 and 108 are components in a backhaul infrastructure.More generally, the access point 104 includes any computing devicesuitable to deploy a wireless local-area network (WLAN). The clientdevice 108, meanwhile, includes any computing device suitable to jointhe above-mentioned WLAN.

The AP 104 and client 108 include respective central processing units(CPU) 110 and 150, also referred to as processors 110 and 150. Theprocessors 110 and 150 are interconnected with respective non-transitorycomputer readable storage media, such as memories 112 and 152, havingstored thereon various computer readable instructions for performingvarious actions. The memories 112 and 152 each include a suitablecombination of volatile (e.g. Random Access Memory or RAM) andnon-volatile memory (e.g. read only memory or ROM, Electrically ErasableProgrammable Read Only Memory or EEPROM, flash memory). The processors110 and 150 and the memories 112 and 152 each comprise one or moreintegrated circuits.

The AP 104 and client 108 also include respective input and outputassemblies 114 and 154. The input and output assemblies 114 and 154serve to receive commands from operators of the devices to control theoperation thereof, and to present information, e.g. to theabove-mentioned operators. The input and output assemblies 114 and 154therefore include any suitable combination of keyboards or keypads,mice, displays, touchscreens, speakers, microphones, and the like. Inother embodiments, the input and output assemblies 114 and 154 may beconnected to the processors 110 and 150 via a network, or may simply beomitted. For example, the access point 104 may omit the input/outputassembly 114.

The AP 104 and client 108 further include respective wirelesscommunications assemblies 116 and 156 interconnected with the processors110 and 150. The assemblies 116 and 156 enable the AP 104 and client108, respectively, to communicate with other computing devices,including each other. In the present example, the assemblies 116 and 156enable such communication according to wireless standards employingfrequencies of around 60 GHz (also referred to as WiGig) and widechannel bandwidths (e.g. exceeding 1 GHz per channel). Examples of suchstandards are the IEEE 802.11ad standard, and enhancements thereto (e.g.802.11ay). The assemblies 116 and 156 can also be configured to enablecommunications according to a variety of other standards, however,including other members of the 802.11 family of standards.

The communications assemblies 116 and 156 include respective controllers118 and 158 in the form of one or more integrated circuits, configuredto establish and maintain communications links with other devices (e.g.,the link 112). The controllers 118 and 158 are configured to processoutgoing data for transmission via respective antenna arrays 120 and 160(e.g. each including a phased array of antenna elements) and to receiveincoming transmissions from the arrays 120 and 160 and process thetransmissions for communication to the processors 110 and 150. Thecontrollers 118 and 158 can therefore each include a baseband processorand one or more transceivers (also referred to as radio processors),which may be implemented as distinct hardware elements or integrated ona single circuit.

In order to enable communications with another device, each of the AP104 and the client 108 is configured to implement various functions toestablish a communications link such as the link 112 shown in FIG. 1.Among the functions implemented by the AP 104 and client 108 is amechanism permitting the devices to detect one another in order toinitiate the establishment of a beamformed connection such as the link112.

As will be apparent to those skilled in the art, wireless communicationdevices that employ beamforming include antenna arrays (such as thearrays 120 and 160 shown in FIG. 1) that can be controlled to transmitor receive according to a variety of radiation patterns. The radiationpatterns may also be referred to as sectors, and the controllers 118 and158 can store sets of configuration parameters corresponding to eachsector. A given sector can be activated, in other words, by applying thecorresponding configuration parameters to the relevant antenna array.

Turning briefly to FIG. 2, the AP 104 and client 108 are shown withexample sectors. In particular, the AP 104 is illustrated with fourexample AP sectors 200-1, 200-2, 200-3 and 200-4, as well as with an APquasi-omni sector 204. A variety of additional sectors and/or quasi-omnisectors can also be implemented by the AP 104, and those shown in FIG. 2are provided solely for illustrative purposes. The client 108 is alsoillustrated with four example client sectors 210-1, 210-2, 210-3 and210-4, as well as a quasi-omni client sector 214. The quasi-omni sectors204 and 214 have greater beam angles than the sectors 200 and 210 (whichmay also be referred to as directional sectors). The quasi-omni sectors204 and 214, however, also have smaller effective ranges than thedirectional sectors 200 and 210.

Before the link 112 has been established, the AP 104 transmits beaconframes. If the client 108 uses the quasi-omni sector 214 to detect thebeacons, the client 108 may be unable to detect the beacons beyondcertain distances from the AP 104 (e.g. about 300 m for 802.11adcommunications). Similarly, the AP 104 may use the quasi-omni sector 204to detect requests to initiate connections from client devices such asthe client 108, but if the client 108 is sufficiently distant from theAP 104, the AP 104 may fail to detect such requests.

Reception of a beacon at the client 108 over such distances may befeasible using a directional sector 210, and reception of a request toinitiate a connection at the AP 104 over such distances may be feasibleusing a directional sector 200. Therefore, the AP 104 and the client 108are each configured to perform various actions to detect whichdirectional sector 200 and 210 to employ for initiation of a connection.In other words, the functionality implemented by the AP 104 and theclient 108, to be discussed in detail herein, enables the AP 104 andclient 108 to avoid relying on the quasi-omni sectors 204 and 214 toestablish connections.

Turning now to FIG. 3, a method 300 for directional scanning andconnection will be discussed in connection with its performance withinthe system 100. In particular, certain blocks of the method 300 areperformed by the AP 104, while other blocks of the method 300 areperformed by the client 108, as indicated in FIG. 3.

It is assumed, at the initiation of the performance of the method 300,that the AP 104 and the client 108 have not established a connectionsuch as the link 112. At block 305 the client 108 selects, from amongthe client sectors 210, an active sector to use for operating in areceiving (RX), or listening, mode to detect a beacon from the AP 104.Of particular note, the quasi-omni sector 214 is omitted from the set ofsectors employed to set an active sector at block 305. That is, theclient 108 employs only the directional sectors 210 at block 305.Further discussion of the selection of a sector at block 305 will beprovided further below.

At block 310, the client 108 (e.g. the controller 158 more specifically)determines whether a beacon has been detected using the sector set atblock 305. When the determination is negative, the client 108 returns toblock 305 to select the next active sector 210 to use in the listeningmode. In other words, the client 108 cycles through the sectors 210,omitting use of the quasi-omni sector 214, to listen for beacons fromthe AP 104.

At block 315, the AP 104 sends a plurality of beacon instances. Forexample, the AP 104 can control the antenna array 120 to transmit abeacon frame using each sector 200, such that if the antenna array 120has sixteen sectors, sixteen beacons are transmitted in succession. Thebeacons contain various information employed by the client 108 and otherclient devices to establish connections with the AP 104. Suchinformation includes a network address of the AP 104, an identifier ofthe WLAN implemented by the AP 104, and the like. Each beacon alsoincludes a sector identifier, corresponding to the sector 200 used totransmit that beacon.

In addition, the beacons transmitted at block 315 contain rotationschedule data. The rotation schedule data defines a plurality oflistening time slots corresponding to respective AP sectors 200. Ratherthan listening for client connection requests using the quasi-omnisector 204, the AP 104 listens for client connection requests using thedirectional sectors 200 in sequence. The rotation schedule data definesthat sequence. The transmission of the rotation schedule data in thebeacons enables any client devices that receive a beacon to determinewhen the AP 104 will be listening on a given sector 200, as will bediscussed further below. In other examples, the rotation schedule dataneed not be contained in the beacons themselves but is otherwiseassociated with the beacons. For example, the client 108 can storepredetermined rotation schedule information, or can retrieve therotation schedule information from another source (e.g. another clientdevice).

Turning to FIGS. 4A, 4B and 4C, examples of the above-mentionedlistening time slots are illustrated. As will be apparent to thoseskilled in the art, the AP 104 implements, in the above-mentioned WLAN,a beacon header interval (BHI) during which beacons are sent, and a datatransmission interval (DTI) during which the AP 104 and client devicescan exchange data. The listening time slots defined in the rotationschedule data are implemented during the DTI. FIGS. 4A-4C eachillustrate an example division of the DTI into listening time slots,with an identifier of a given sector 200 indicating which sector 200 isactive during the relevant time slot.

In the example of FIG. 4A, the DTI is divided into a number of listeningtime slots equal to the number of available sectors 200, excluding thequasi-omni sector 204. The AP 104 rotates through each of the sectors200-1 to 200-4 in a listening mode during a single DTI. In thesubsequent DTI, the rotation is therefore repeated. In other words,during each DTI the AP 104 activates the listening mode using eachsector 200 for one quarter of the DTI. As will be apparent, the DTI maybe subdivided into smaller slots for greater numbers of sectors 200.

In the example of FIG. 4B, the same subdivision of the DTI into fourslots is employed as in FIG. 4A. However, the activation of thelistening mode is offset by one slot. That is, a slot 400 is notassigned to any sector 200 and the AP 104 does not activate thelistening mode during the slot 400. Rotation through the sectors 200therefore consumes more than one DTI, with the sector 200-4 beingactivated in the second DTI as shown in the illustration.

In the example of FIG. 4C, the DTI is subdivided into two slots ratherthan four, with the result that two DTIs are used to accommodaterotation through the four sectors 200. As will now be apparent, a widevariety of other arrangements can also be implemented to subdivide theDTI into listening time slots and assign such slots to specific sectors200. For example, in another embodiment a single one of the sectors 200can be assigned to each DTI, such that rotating through each sector 200requires four DTIs (and four associated beacon transmissions).

The beacons transmitted at block 315, as noted above, contain rotationschedule data defining the arrangement of listening time slotsimplemented by the AP 104. An example of the rotation schedule data isshown in FIG. 5. In particular, FIG. 5 illustrates a beacon frame 500including an information element (IE) 504 containing the rotationschedule data. The IE 504 can also be included in other control frames,such as probe and association frames.

The IE 504 includes various fields. In the illustrated example, thefields of the IE 504 include a directional beam scan and connect (DBSC)header, which may for example indicate the start and the length of theIE 504. The fields can also include a version number field 508, in theevent that multiple versions of the IE 504 exist with different content.

In addition, the IE 504 can include a flags field 510, containing astring of bits each indicating whether a corresponding feature isenabled or disabled. An example of such features include whetherrotation is enabled or disabled. Another example of a featurerepresented in the flags field 510 is a bit indicating whether the AP104 is currently implementing the above-mentioned activation ofsuccessive sectors 200 according to the listening time slots. As will beseen below, under certain conditions the activation of a listening modewhile rotating through the sectors 200 can be temporarily paused by theAP 104. Another example flag in the field 510 is a bit indicatingwhether the AP 104 has (e.g. temporarily) fixed the sector 200 on whichthe AP 104 is listening, which also results in pausing theabove-mentioned rotation. As will be apparent, the previous two bits aremutually exclusive (i.e. if the rotation feature is active, the fixedfeature is not active). Various other features are also contemplated forindication in the field 510. Examples of such features include whetherthe AP 104 has fixed the sector 200 on which the AP 104 is listening fora preconfigured timeout period.

In the example of FIG. 5, the IE 504 also includes a rotation indexfield 512, indicating an index of the current beacon relative to thetotal number of beacons that accommodate a full rotation through thesectors 200. For example, in the case of the implementation shown inFIG. 4A the index field 512 can simply be omitted, or can be set to zeroin every beacon 500. For the example implementation of FIG. 4C, however,in which a full rotation through the sectors 200 takes two beaconintervals, the index field 512 may contain a zero in the first beacon,and a one in the next beacon. For an implementation that takes fourbeacons to complete a rotation through the sectors 200, the index field512 in successive beacons may values of zero, one, two and three,followed by a return to zero.

The IE 504 can also include an offset field 514 indicating, for example,a time between the start of the DTI and the first listening time slot.Such an offset is zero for the examples shown in FIGS. 4A and 4C, butnon-zero for the example shown in FIG. 4B. The IE 504 can also include acount field 516, indicating a number of listening time slots to beimplemented in the coming DTI, and a duration field 520 indicating thelength (e.g. in time units (TU), each equivalent to 1024 microseconds)of each listening time slot. Other information can also be included inthe IE 504, such as a total number of listening time slots (which is notnecessarily equal to the number of slots in a given DTI).

Various formats and content may be implemented for the IE 504.Generally, as will be apparent from the discussion above, the rotationschedule data in the beacons sent at block 315 contains sufficientinformation for any client device receiving a beacon to determine, foreach listening time slot, both the timing of that slot and which sector200 will be active during that slot.

Returning to FIG. 3, at block 320 following transmission of the beaconsat block 315, the AP 104 implements the listening rotation defined inthe rotation schedule data. That is, the AP 104 selects a first sector200 to activate in a listening mode. At block 325 the AP 104 determineswhether any client transmissions (e.g. a sector-level sweep, SLS) havebeen detected using the active sector 200. When the determination isnegative, the AP 104 selects the next active sector 200 according to therotation schedule data at block 320. In addition, as indicated by thedashed line to block 315, the AP 104 may transmit additional beaconsdepending on the configured timing of the beacons and the rotationschedule data.

As noted earlier, during transmission of the beacons and the rotatinglistening mode at the AP 104, the client 108 rotates through the sectors210 in a listening mode via successive performances of blocks 305 and310. The client 108 can activate each sector 210 for a configurableperiod of time. For example, the client 108 can activate each sector 210for 100 TU, which is also the default beacon interval employed by manyAPs. Various other time periods may also be employed, however.

When a beacon is detected at block 310 (e.g. using the sector 210-3),the client 108 proceeds to block 330. At block 330, based on therotation schedule data in the received beacon, the client 108 determinesthe timing of the listening time slot at the AP 104 that corresponds tothe AP sector 200 used to transmit the beacon. That is, assuming thatthe beacon received at block 310 indicates that it was transmitted usingthe sector 200-2, the client 108 determines when the sector 200-2 willbe activated by the AP 104 in a listening mode, based on the rotationschedule data. The determination at block 330 reflects an assumptionthat the sector 200 used to transmit the beacon that successfullyreached the client 108 will also enable the AP 104 to successfullyreceive communications from the client 108.

The determination at block 330 can be made via any of a variety ofmechanisms. For example, beacons can indicate a target beacontransmission time (TBTT), indicating times at which beacons aretransmitted by the AP 104. The TBTT, and information in the beacondefining the start of a DTI relative to the TBTT, enables the client 108to determine when the listening time slots begin at the AP 104. Thetiming of the start of each listening time slot can be determined basedon the slot duration and count values, e.g. from the fields 520 and 516.Further, which slot corresponds to the relevant sector 200 (i.e. thesector 200 that was used to transmit the received beacon) can bedetermined according to the count and index fields 516 and 512.

At block 335, when the time determined at block 330 arrives (i.e, whenthe AP 104 is listening using the same sector 200 that was used totransmit the beacon received at block 310), the client 108 sends acommunication to the AP 104. The communication can be a messageinitiating a sector level sweep (SLS), in some examples.

The AP 104, as noted earlier, awaits a transmission such as the SLSinitiation at block 325. When the determination at block 325 isaffirmative, the AP 104 proceeds to block 340. At blocks 340 and 345,the AP 104 and the client 108, respectively, exchange messages to selectsectors 200 and 210 for use in further communications. For example, theclient 108 may transmit data using each of the sectors 210 and the AP104 may indicate to the client 108 which sector 210 resulted in thestrongest received signal at the AP 104. The above process may also berepeated in the opposite direction, with the AP 104 transmitting datausing each sector 100 and the client 108 indicating which sector 200resulted in the strongest received signal at the client 108.

To conclude the performance of blocks 340 and 345, the AP 104 and theclient 108 set the sectors 200 and 210, respectively, identified throughblocks 340 and 345. Different sectors 200 and 210 may be set oftransmission and reception, or the same sector 200/210 may be employedfor both transmission and reception.

The performance of block 345 can also include any other suitableprocedures for initiating communication between the client 108 and AP104, such as the transmission of probe frames. The client 108 may alsoreturn to block 305 if a connection is not required at block 345.

At block 350, the AP 104 pauses rotation through the sectors 200 in alistening mode according to the rotation schedule data. Instead, the AP104 is configured to activate the listening mode using only the sector200 identified via the performance of blocks 340 and 345. Any beaconstransmitted while rotation is paused can include a value (e.g. in theflags field 510) indicating that the AP 104 has temporarily fixed thesector 200 on which the AP 104 is listening.

At block 355, the AP 104 determines whether a connection request hasbeen received. When no connection request is received, e.g. within aconfigurable time period, the pause on rotation is released and the AP104 returns to block 315. When a connection request is received at block355, e.g. a connection request sent by the client 108 at block 360, theAP 104 proceeds to block 365. As will now be apparent, the connectionrequest sent at block 360 by the client 108 is sent using the sectorselected at block 345.

At blocks 365 and 370, the AP 104 and the client 108 exchange data toestablish a connection such as the link 112 shown in FIG. 1. The AP 104can also continue to perform the method 300 following establishment ofthe connection, to enable other client devices to detect the AP 104 andrequest connections. When one or more client devices are connected tothe AP 104, subsequent performances of the method 300 can employmodified rotation schedule data that allocates only a portion of the DTIto the rotating listening mode discussed above. The remainder of the DTIcan be allocated to data exchange over existing connections to clientdevices. For example, the offset (e.g. illustrated in FIG. 4C) can beincreased.

The scanning and connection mechanisms set out above may enable the AP104 and the client 108 to discover one another and establish the link112 at distances greater than may be achievable using the quasi-omnisectors 204 and 214.

Additional variations to the above mechanisms are contemplated. Forexample, in some implementations the AP 104 and the client 108 canperform further actions that may accelerate the detection of a beacon bythe client 108. In such implementations, as shown in FIG. 6, the AP 104may transmit, in addition to the beacons discussed above, an auxiliarybeacon 600. The auxiliary beacon 600 can be, for example, asector-sweep-to self (SSW-to-self), a discovery DMG beacon or the like.That is, the auxiliary beacon 600 need not contain the same data as thebeacons sent at block 315. Instead, the auxiliary beacons 600 cancontain only a subset of the data in the beacons. At minimum, theauxiliary beacon contains sector identifiers. Further, as shown in FIG.6, the auxiliary beacons 600 are sent during the DTI at a configurablefrequency. The auxiliary beacons 600 are transmitted, like the beaconsthemselves, once per sector 200.

The client 108, as shown in FIG. 7, can be configured to determine atblock 705, which occurs after block 305 but before block 310, whether anauxiliary beacon 600 has been detected. When the determination isnegative, the client 108 proceeds to block 310 as described above. Whenthe determination at block 705 is affirmative the client 108 insteadproceeds to block 710 and fixes the current client RX sector 210 beforeproceeding to block 310. In other words, the auxiliary beacons provideadditional opportunities for the client 108 to discover a sector 210 atwhich a beacon may be detectable.

In further examples, the performance of blocks 305 and 310 can berepeated by the client 108 after an initial beacon detection, todetermine whether another sector 210 results in a stronger detection ofa beacon.

In still further variations, the quasi-omni sector 214 need not beomitted from the set of sectors employed to set an active sector atblock 305. That is, the quasi-omni sector 214 can be integrated into therotation discussed above along with the directional sectors 200.

In other embodiments, the AP 104 need not repeat the same rotationschedule for each rotation, e.g. as illustrated in FIG. 4A. For example,the AP 104 can randomize or otherwise vary the order of activation ofthe sectors 200 in the listening mode. In such examples, each beacon caninclude an indication of which listening time slot corresponds to thesector 200 that was used to transmit the beacon. In further examples,the beacon need not include such information, and the client 108 caninitiate a sector sweep at block 335 for each listening time slot ratherthan determining which slot to wait for at block 335.

In further embodiments, when the BHI includes a portion allocated toassociation beamforming training (ABFT), the AP 104 can also beconfigured to divide the ABFT period into listening time slots asdescribed above in connection with the DTI.

The scope of the claims should not be limited by the embodiments setforth in the above examples, but should be given the broadestinterpretation consistent with the description as a whole.

1. A method in a wireless access point (AP) having an antennacontrollable to transmit and receive using a set of AP sectors, themethod comprising: transmitting a plurality of beacon instances usingeach of the AP sectors, each beacon instance associated with rotationschedule data defining a plurality of listening time slots correspondingto respective AP sectors; activating a rotating listening mode using theAP sectors in sequence according to the rotation schedule data; inresponse to detecting a sector sweep initiation message from a clientdevice using an active one of the AP sectors, communicating with theclient device to select an AP sector to use in establishing a link withthe client device.
 2. The method of claim 1, further comprising: inresponse to communicating with the client device to select an AP sectorto use for communicating with the client device, activating a fixedlistening mode using the selected AP sector; determining whether aconnection request has been received from the client device; and when aconnection request is received, establishing a connection with theclient device.
 3. The method of claim 2, further comprising: when noconnection request is received within a predetermined time period,returning to activating the rotating listening mode using the AP sectorsin sequence according to the rotation schedule data.
 4. The method ofclaim 2, further comprising: during activation of the fixed listeningmode, transmitting a further plurality of beacon instances, each beaconinstance containing the rotation schedule data and an indication thatthe rotating listening mode is paused.
 5. The method of claim 1, whereinthe rotation schedule data is contained in an information element ofeach beacon instance.
 6. An access point, comprising: an antenna arraycontrollable to transmit and receive using a set of AP sectors; acontroller connected to the antenna array and configured to: control theantenna array to transmit a plurality of beacon instances using each ofthe AP sectors, each beacon instance associated with rotation scheduledata defining a plurality of listening time slots corresponding torespective AP sectors; activate a rotating listening mode using the APsectors in sequence according to the rotation schedule data; and inresponse to detection of a sector sweep initiation message from a clientdevice using an active one of the AP sectors, communicate with theclient device to select an AP sector to use for establishing a link withthe client device.
 7. The access point of claim 6, wherein thecontroller is further configured to: in response to communicating withthe client device to select an AP sector to use for communicating withthe client device, activate a fixed listening mode using the selected APsector; determine whether a connection request has been received fromthe client device; and when a connection request is received, establisha connection with the client device.
 8. The access point of claim 7,wherein the controller is further configured to: when no connectionrequest is received within a predetermined time period, return toactivating the rotating listening mode using the AP sectors in sequenceaccording to the rotation schedule data.
 9. The access point of claim 7,wherein the controller is further configured to: during activation ofthe fixed listening mode, transmit a further plurality of beaconinstances, each beacon instance containing the rotation schedule dataand an indication that the rotating listening mode is paused.
 10. Theaccess point of claim 6, wherein the rotation schedule data is containedin an information element of each beacon instance.
 11. A method in awireless client device having an antenna controllable to transmit andreceive using a set of client sectors, the method comprising: activatinga rotating listening mode using the client sectors in a predefinedsequence; in response to detecting a beacon from an access point (AP)associated with rotation schedule data defining a plurality of listeningtime slots corresponding to respective AP sectors of the AP, determininga transmission time based on the rotation schedule data; and at thetransmission time, transmitting a message to the AP.
 12. The method ofclaim 11, wherein determining the transmission time includes:identifying, from the beacon, one of the AP sectors used to transmit thebeacon; identifying one of the listening time slots that corresponds tothe one of the AP sectors; and computing, according to the rotationschedule data, a scheduled time for the identified listening time slot.13. A wireless client device, comprising: an antenna array controllableto transmit and receive using a set of client sectors; a controllerconnected to the antenna array and configured to: activate a rotatinglistening mode using the client sectors in a predefined sequence; inresponse to detecting a beacon from an access point (AP) associated withrotation schedule data defining a plurality of listening time slotscorresponding to respective AP sectors of the AP, determine atransmission time based on the rotation schedule data; and at thetransmission time, transmit a message to the AP.
 14. The wireless clientdevice of claim 13, wherein the controller is configured, in order todetermine the transmission time, to: identify, from the beacon, one ofthe AP sectors used to transmit the beacon; identify one of thelistening time slots that corresponds to the one of the AP sectors; andcompute, according to the rotation schedule data, a scheduled time forthe identified listening time slot.